Day began his career with Crystal Palace before joining Rushden & Diamonds in 2007. After spending time out on loan at Harrow Borough Day established himself in the Rushden & Diamonds first team. He joined Peterborough United in April 2011 and spent most of the season on loan at Alfreton Town. In August 2014, Day joined League Two Newport County on a one-month loan, but they later agreed a full transfer with Peterborough United. Day was part of the Newport squad that completed the 'Great Escape' with a 2–1 victory at home to Notts County on the final day of the 2016–17 season, which ensured Newport's survival in League Two. In June 2019, Day signed a two-year deal with Cardiff City following the expiry of his contract at Newport. And later joined AFC Wimbledon on a six-month loan in January 2020. In January 2021, Day joined Bristol Rovers on loan until the end of the season. In June 2021, Day returned to former club Newport County, signing a three-year contract two years after he had left the club to join Cardiff City. He made his third debut for Newport on 7 August 2021 in the starting line-up for the 1–0 League Two win against Oldham Athletic.